The Consistency dimension and distribution-dependent learning from queries

We prove a new combinatorial characterization of polynomial learnability from equivalence queries, and state some of its consequences relating the learnability of a class with the learnability via equivalence and membership queries of its subclasses obtained by restricting the instance space. Then we propose and study two models of query learning in which there is a probability distribution on the instance space, both as an application of the tools developed from the combinatorial characterization and as models of independent interest.Postprint (published version

Approaching the precursor nuclei of the third r-process peak with RIBs

The rapid neutron nucleosynthesis process involves an enormous amount of very exotic neutron-rich nuclei, which represent a theoretical and experimental challenge. Two of the main decay properties that affect the final abundance distribution the most are half-lives and neutron branching ratios. Using fragmentation of a primary 238U beam at GSI we were able to measure such properties for several neutron-rich nuclei from 208Hg to 218Pb. This contribution provides a short update on the status of the data analysis of this experiment, together with a compilation of the latest results published in this mass region, both experimental and theoretical. The impact of the uncertainties connected with the eta-decay rates and with beta-delayed neutron emission is illustrated on the basis of r-process network calculations. In order to obtain a reasonable reproduction of the third r-process peak, it is expected that both half-lives and neutron branching ratios are substantially smaller, than those based on FRDM+QRPA, commonly used in r-process model calculations. Further measurements around N 126 are required for a reliable modelling of the underlying nuclear structure, and for performing more realistic r-process abundance calculations.Postprint (published version

A structural study of the behavior of bumper cars compared to a system of spatially uncorrelated hard disks

2014/201

Tafonomía, taxonomía y ecología de los foraminíferos de la Albufera de Torreblanca.

RESUMEN En este trabajo se aborda el estudio de los foraminíferos de la albufera de Torreblanca desde un triple punto de vista: taxonómico, ecológico y tafonómico. Se estudió el contenido en foraminíferos de 46 muestras, cada una de ellas con un volumen fijo de 3 cm3 de sedimento. Las muestras fueron recogidas por raspado superficial en 9 puntos de muestreo situados en las lagunas de aguas salobres permanentes, originadas por la extracción industrial de turba en el sector norte del Prat de Cabanes-Torreblanca. En dos de estos puntos se realizó un muestreo mensual a lo largo del año 1993, mientras que de los restantes se recogieron muestras en los meses de enero, mayo y agosto. Paralelamente se llevó a cabo la medición de una serie de parámetros físico-químicos en el agua de las lagunas entre los que se incluyó la temperatura, salinidad, alcalinidad, el pH y el contenido en oxígeno y diversos iones. El método de tinción con rosa de Bengala permitió separar las asociaciones formadas por foraminíferos vivos en el momento del muestreo (biocenosis) de aquellas constituidas por foraminíferos muertos o caparazones vacíos (tanatocenosis). Se han encontrado en total 18 especies de foraminíferos repartidas en 6 órdenes distintos, algunas de las cuales (Disconorbis bulbosus, Laminononion tumidum, Turrispirillina sp. o aff. Physalidia sp.) no se han citado con anterioridad en ambientes restringidos. Los foraminíferos de caparazón calcáreo hialino son predominantes, en particular Trichohyalus aguayoi y D. bulbosus y en menor medida Spirillina vivipara, aff. Physalidia sp. y Ammonia beccarii var. tepida. Como es frecuente en ambientes parálicos, las asociaciones de foraminíferos se caracterizan por una densidad muy variable, una baja diversidad y la abundancia de ejemplares de tamaño reducido y de especies pequeñas. Tanto el estrecho rango de variación de los parámetros ambientales entre las distintas estaciones de muestreo como el amplio rango de tolerancia de los foraminíferos de ambientes restringidos impiden la delimitación de subambientes en el área de estudio a partir de las asociaciones de foraminíferos y explican el, en general, bajo nivel de correlación entre éstas y dichas variables ambientales. Los datos son compatibles con un modelo según el cual las distintas especies no compiten entre sí si no que reaccionan de forma conjunta ante un mismo factor, fluctuando de manera aperiódica y asincrónica con las mismas especies de agregados vecinos. Las distintas técnicas estadísticas empleadas (análisis cluster, de componentes principales, y de correlación) permiten diferenciar dos asociaciones de especies: la primera asociación podría estar ligada a una mayor influencia continental e incluye especies relacionadas con ambientes de marjal alto o medio, como T. aguayoi, Trochammina inflata, Jadammina macrescens y Haplophragmoides wilberti; la segunda asociación podría estar ligada a una mayor influencia marina e incluye especies relacionadas con ambientes de marjal bajo, como A. beccarii var. tepida, Elphidium sp. y Miliammina fusca. Los procesos tafonómicos que actúan sobre los caparazones de foraminíferos y que se han puesto de manifiesto son: distorsión tafonómica, que da lugar a alteraciones de tipo mecánico, precipitado de CaCO3 sobre la superficie de las conchas calcáreas, rellenos sedimentarios y de pirita, bioerosión, crecimientos cristalinos y encostramientos biogénicos. El entorno geológico, constituido mayoritariamente por materiales calcáreos determina las condiciones físico-químicas del agua de las lagunas (pH básico y alta alcalinidad), que favorecen la conservación de las conchas de CaCO3, mientras que existe un proceso de destrucción diferencial de las conchas de pared aglutinada sobre base orgánica. La alta afinidad entre biocenosis y tanatocenosis es la esperable en ambientes restringidos como las lagunas costeras con un bajo hidrodinamismo, en las que la mezcla de caparazones de procedencias distintas o el transporte no son factores importantes. __________________________________________________________________________________________________The benthic foraminifera of the Cabanes-Torreblanca coastal lagoon (Comunitat Valenciana, Spain) have been studied following taxonomical, ecological and taphonomical approaches. Nine sampling localities were chosen in the northern sector of the brackish lagoon. In seven of them, three seasonal surface samplings were carried out (January, May and August), whereas in the two remaining sites, sampling was done monthly through the year 1993. Additionally, different environmental variables (temperature, salinity, alkalinity, pH, oxygen and ionic content) were analyzed. The Rose Bengal staining method allowed the distinction between the living and dead assemblages. Eighteen species have been identified, some of which (Disconorbis bulbosus, Laminononion tumidum, Turrispirillina sp. or aff. Physalidia sp.) not previously recorded in restricted environments. The calcareous foraminifera are dominant, in particular Trichohyalus aguayoi and D. bulbosus and, to a lesser extent Spirillina vivipara, aff. Physalidia sp. and Ammonia beccarii var. tepida. As usual in paralic environments, highly variable density, low diversity and abundance of small-sized forms characterize the assemblages. Both the environmental homogeneity in the lagoon and the characteristic wide tolerance range of the foraminifera from restricted environments prevent the distinction of sub-environments within the study area based on foraminiferal assemblages, and explain the low correlation between environmental variables and foraminifers. Nevertheless, the different statistical techniques employed (cluster analysis, PCA, correlation) reveal two main assemblages. The first one might be linked to a greater continental influence and includes high or middle marsh species like T. aguayoi, Trochammina inflata, Jadammina macrescens and Haplophragmoides wilberti, whereas the second one might be related to the marine influence and comprises low marsh species like A. beccarii var. tepida, Elphidium sp. and Miliammina fusca. The main taphonomic processes identified are mechanical alterations, deposits of CaCO3 crusts on calcareous shells, sedimentary and pyrite infillings, bioerosion, crystalline growths and biogenic encrustations. The geological setting, mainly constituted by calcareous limestones, determines the low pH and the high alkalinity of the lagoon water, thus preventing CaCO3 dissolution and preserving calcareous shells. The affinity between living and dead assemblages is high, as expected in low energy environments in which transport and shell mixing are not important factors

The BRIKEN Project: extensive measurements of ß-delayed neutron emitters for the astrophysical r process

An ambitious program to measure decay properties, primarily ß-delayed neutron emission probabilities and half-lives, for a significant number of nuclei near or on the path of the rapid neutron capture process, has been launched at the RIKEN Nishina Center. We give here an overview of the status of the project.Postprint (published version

Two [Ln(4)] molecular rings folded as compact tetrahedra

The design of photoactive ligands may provide access to multifunctional molecular nanomagnets. Wereport here the design and synthesis of a new multitopic chelating ligand, 1,2-bis-(5-(N'-(pyridine-2-yl-methylene)-carbohydrazide)-3-methyl-thien-3-yl)-cyclopentene (H2L), bearing a photoswitchablespacer and demonstrate that it undergoes reversible photoisomerization in solution. In the presence ofthe base NaH, H2L reacts with LnCl3salts (Ln = Dy, Tb) to form the supramolecular assemblies H2O@[Ln4L4Cl4(H2O)4] (Ln = Dy,1; Tb,2). The single crystal X-ray diffraction data of1and2reveal that bothcompounds consist of highly symmetric molecular rings efficiently folded through intramolecular weakinteractions in the form of tetrahedra. This arrangement imparts a conformation to the photochromicspacer of the ligand which inhibits its photoswitching activity. Despite the low symmetry of the coordi-nation geometry around the Ln ions, the Dy analog exhibits slow relaxation of the magnetization. Therelaxation rate under various conditions has been investigated, allowing us to elucidate the mechanismsinvolved in this relaxation

Advanced CFD&HT numerical modeling of solar tower receivers

This paper presents an advanced methodology for the detailed modeling of the heat transfer and fluid dynamics phenomena in solar tower receivers. It has been carried out in the framework of a more ambitious enterprise which aims at modeling all the complex heat transfer and fluid dynamics phenomena present in central solar receivers. The global model is composed of 4 sub-models (heat conduction, two-phase flow, thermal radiation and natural convection) which are described.Peer ReviewedPostprint (published version

Modelling human behaviour in a bumper car ride using molecular dynamics tools: a student project

Amusement parks are excellent laboratories of physics, not only to check physical laws, but also to investigate if those physical laws might also be applied to human behaviour. A group of Physics Engineering students from Universitat Politècnica de Catalunya has investigated if human behaviour, when driving bumper cars, can be modelled using tools borrowed from the analysis of molecular dynamics simulations, such as the radial and angular distribution functions. After acquiring several clips and obtaining the coordinates of the cars, those magnitudes are computed and analysed. Additionally, an analogous hard disks system is simulated to compare its distribution functions to those obtained from the cars' coordinates. Despite the clear difference between bumper cars and a hard disk-like particle system, the obtained distribution functions are very similar. This suggests that there is no important effect of the individuals in the collective behaviour of the system in terms of structure. The research, performed by the students, has been undertaken in the frame of a motivational project designed to approach the scientific method for university students named FISIDABO. This project offers both the logistical and technical support to undertake the experiments designed by students at the amusement park of Barcelona TIBIDABO and accompanies them all along the scientific process.Postprint (published version

Characterization of coastal upwelling events during the generation of the water column stratification in spring (Vilanova i la Geltrú, NW Mediterranean)

This article presents some preliminary results on the characterization of inputs of offshore waters (upwelling events) in the coast off Vilanova i la Geltrú (NW Mediterranean) in the spring of the years 2010, 2012 and 2014. The upwelling events are studied in terms of meteorological and oceanographic conditionsPostprint (author’s final draft